In a trench gate MOS field effect transistor (MOSFET), as compared with a planer gate MOSFET, reduction of on-resistance due to reduction of cell pitch can be expected. In a trench gate MOSFET using a wide band gap semiconductor such as silicon carbide (SiC) as a material, structures using an a-plane (11-20) on a sidewall surface of a trench have been proposed (refer to US 2017/0,077,251 A (Patent Literature 1), JP 6105032 B2 (Patent Literature 2), and JP 2016-163047 A (Patent Literature 3)). In Patent Literatures 1 to 3, an n-type source region and a p-type base region are provided on one sidewall surface of a trench, and the sidewall surface is used as a current path.
In an insulated-gate semiconductor device such as a trench gate MOSFET using a wide band gap semiconductor as a material, further improvement of the structure of the insulated-gate semiconductor device and the method of manufacturing the insulated-gate semiconductor device is required.